In modern processors, power consumption is in direction proportion to the frequency at which a processor (or core) operates. Reducing consumption thus can be achieved by reducing core frequency such that frequency control provides a means to control processor power consumption. However, that reduction unconditionally applied would result in degraded system performance.
In contrast, when a processor (or core) runs at a fixed frequency, it uses more power than necessary while running at reduced loads, where its utilization is less than 100%. Thus many systems provide some type of frequency control. Typically, frequency control is done using an operating system (OS) mechanism such as an Advanced Configuration and Power Interface (ACPI)-based mechanism. However, there are drawbacks to this approach, including the latency needed to monitor the processor and change frequency, as well as the coarse manner in which it is performed.